From http://www.microsoft.com/windowsxp/u...noverview.mspx
The Remote Desktop Web Connection is a high-encryption, Remote Desktop Protocol (RDP) 5.0 client and uses RSA Security's RC4 cipher with a key strength of 40-, 56-, or 128-bit, as determined by the computer to which it is connecting. The Remote Desktop Web Connection uses the well-known RDP TCP port (3389) to communicate to the host. Unlike some other display protocols, which send data over the network using clear text or with an easily decodable "scrambling" algorithm, Remote Desktop Web Connection's built-in encryption makes it safe to use over any network—including the Internet—as the protocol cannot be easily sniffed to discover passwords and other sensitive data.